It is well known in the rubber industry that preferred accelerators are those which, when mixed into vulcanizable rubber compositions and heated, exhibit an induction period (scorch delay) prior to the onset of vulcanization. It is also preferred that vulcanization proceed rapidly once the induction period has ended. Such a combination of characteristics has the practical benefits of maximum processing safety and shorter cure cycles. The present invention provides novel accelerator systems which meet these criteria.
It is also well known in the rubber industry that unsaturated rubbers are subject to attack by ozone, resulting in surface cracks which can penetrate to the point of failure of the rubber article. Common practice is to add chemical antiozonants, usually p-phenylenediamine derivatives to the rubber to help resist ozone attack. Such phenylenediamines, however, cause severe discoloration and are thus unsuitable for white or light colored rubbers. The compounds of the present invention can be used to provide ozone protection without causing the usual discoloration.
The cyanamides useful in the compositions of the present invention may be synthesized by adaptations of prior art procedures, wherein cyanamide, H.sub.2 N--C.dbd.N, is reacted with two molar equivalents of an organohalide, RX, to produce an N,N-disubstituted cyanamide, R.sub.2 NCN. Examples of N,N-disubstituted cyanamide production can be found in A. Jonczyk, Z. Ochal, and M. Makosza, Synthesis, 1978, p. 882. and U.S. Pat. No. 4,206,141 (June 3, 1980).